273 302 318 340 build

DCR is a computed value; hand computations are complex as it involves the crank stroke and rod length, and computes the remaining stroke left on the compression stroke when the intake valve finally closes.

There are various DCR calculators: I use the Pat Kelley calculator (free, online), as it will do both SCR and then use that result along with cam entry data to compute DCR, all in one tool. Wallace has a DCR calculator but you have compute SCR separately first.

The big variable in the intake closing angle is the cam duration and the cam timing. With a solid, like your 270, you also back off advertised duration a bit to compensate for the effect of valve lash, which makes the intake closing angle a bit earlier.

FWIW.... Going back through the Pat Kelley calculator, using:
- the unmilled 302 heads (64 ccs)
- a .028" thick head gasket
- a 265 intake cam duration (shorter than the 270 advertised to account for the lash)
- 106 ICL
- the 526 pistons
I get 8.9 SCR and 7.4 DCR; that DCR is fair to decent for low RPM torque, But I would like to be up near 8.

Going with the 285 pistons, I get SCR/DCR of 7.8/6.6. That DCR is not going to be good for low RPM torque. The Wallace DCR calculator shows that 6.6 DCR translates to around 120 psi.... stone stock 318 numbers...ooops.

With the the SCR pushed up to 9.4, by milling the heads for 59 cc chambers, and using the 526 pistons, you get an SCR of 9.4. Now DCR is 7.8, and cranking compression will be 150-155 psi. THAT is gonna have good low RPM torque!